A wide variety of industrial operations require the use of various process gases. In some of these operations, the process gases may be purchased and/or stored in bulk quantities and supplied via a direct pipeline from the producer. In many cases, however, the quantity of gas required does not warrant purchasing or storing the gases in bulk quantities. In other cases, the gases may not be available in bulk quantities.
When it is not desirable to purchase process gases in bulk quantities, or when a particular gas is not available in bulk quantities, the gas is typically supplied in a pressurized cylinder or tank. As used herein, the term "gas cylinder" includes cylinders and tanks used to store liquified gases and gases absorbed or contained in media inside the cylinder or tank as well as cylinders or tanks used to store material in the gas phase. Such cylinders or tanks can range in size from 5.0 Kg. to 500 Kg. and larger. In some applications a number of different process gases will be supplied in cylinders and these cylinders will be placed at various locations in the manufacturing facility. For example, in the semiconductor fabrication industry, a variety of process gases used for different process steps are typically supplied in cylinders.
In order to control costs, it is desirable to maintain on hand only the am6unt of raw materials, including process gases, necessary to insure continuity of operations. On the other hand, unplanned process shutdowns or interruptions resulting from depletion of required raw materials can be extremely costly and detrimental to operations. Thus, there is a need for an improved system to maintain inventory control over process gases supplied in cylinders.
Additionally, many process gases are toxic, flammable or incompatible with other raw materials. In such cases it is desirable to insure that only the correct process gas is utilized in a given process step. Thus there is a need for an improved gas cylinder monitoring system that has the capability of preventing a cylinder containing the wrong gas from being utilized in a particular process step.